High brightness light emitting diodes such as blue, green, white etc. are already put to practical use by the accumulation of essential technology such as cold deposited buffer layer technology, p-type conductivity control, n-type conductivity control, high efficiency emitting layer etc. In an existing light emitting diode, to increase the light extraction is the problem since refractive index of semiconductor is larger than refractive index of air etc. and, thus, most of light can not be taken off to the outside of the light emitting diode by total reflection or Fresnel reflection.
For solving this problem, a concavo-convex structure which is worked on the semiconductor surface in several micrometer period is proposed (for example, see the non-patent literature 1). When a concavo-convex structure is provided at an extraction side of the semiconductor surface, the total reflection is lost by the light scattering effect and about 50% transmission can be obtained in the relatively wide radiation angle, thus, the light extraction efficiency can be improved to about 50%.
Also, to increase the light extraction by providing the period of the concavo-convex structure which is equal to or smaller than twice the optical wavelength is proposed(for example, see the patent literature 1). In this case, the mechanism for extracting light differs from the period of several micrometer of the concavo-convex structure. Wave nature of light appears and the border of reflective index disappears, and thus, Fresnel reflection is suppressed. Such structure is called photonic crystal or moth-eye structure and can increase the light extraction up to about 50%.